Reference is made first to a number of prior art patent specifications, in the name of the present Applicant or the Applicant in the French application from which priority is claimed in the present case. Notable among these prior art specifications are those of the French documents FR 2 536 502A, FR 2 536 503A, FR 2 583 139A, FR 2 599 120A, FR 2 599 121A, FR 2 600 024A, FR 2 602 305A, FR 2 602 306A, and FR 2 694 373A.
In the prior art represented variously by the above mentioned documents, a motor vehicle headlamp reflector is known which is capable, by cooperating with a generally cylindrical light source which emits light freely all around it, of generating a beam which is delimited by a straight cut-off line at the top or bottom of the beam. By judicious combination of this kind of surface, it is possible to make reflectors which emit beams satisfying various photometric criteria, and in particular, cruising beams and beams for penetrating fog.
It is also known, especially from the further French specifications (in the name of the same Applicant) FR 2 609 146A, FR 2 609 148A, FR 2 639 888A and FR 2 664 677A, to provide reflectors of a second type. In this second type the surfaces are so designed as to provide, as a general rule, the same type of cut-off, while offering beams which are of substantial width and are highly homogeneous. As a result, it is possible to have recourse to headlamp cover glasses which are smooth or only very slightly striated. Such cover glasses are advantageous, both from the optical point of view and from the aesthetic point of view, because the beam which is produced by the single reflector is able to have all the required qualities.
However, the design of that type of reflector does have certain limitations, and in particular it involves, generally, tackling the question of the width of the beam. Thus, with reflectors of the above mentioned second type, it is extended regions of the reflector that, in general, determine the width of the beam.